| Cheese is a kind of fermented dairy products with good nutritional quality and high added value.During cheese ripening,protease from cheese and foreign microbiota will hydrolyze casein and peptides,and produce various kinds of small peptides with functional activity,such as antioxidant peptides,antihypertensive peptides and antibacterial peptides.Studies have shown that the addition of Bifidobacterium and Lactobacillus acidophilus to cheese has the potential to improve the function of cheese.However,whether the bioactive peptides in cheese can keep stable during maturation and can be released from cheese matrix and be absorbed by the body during gastrointestinal digestion is an urgent problem to be studied.Therefore,we studied Bifidobacterium and Lactobacillus acidophilus on the production of cheese antioxidant peptide and explored its stability in the gastrointestinal tract,and the results of this study have some practical guiding significance.The protease activity,tolerance of the gastrointestinal tract,hydrophobicity of and the growth relationship of B.bifidum 07-300B and L.acidophilus 1.0357 in mixed culture were studied.The two strains used in Cheddar cheese,to study its influence on proteolysis and antioxidant activity of cheese.The stability and antioxidant peptide release of cheese after digestion were investigated,and the antioxidant effect of probiotics cheese was verified through animal experiments.The specific contents and results were as follows:(1)The protease activity of B.bifidum 07-300B and L.acidophilus 1.0357 was studied.The results showed that the diameter of casein hydrolysate circle of B.bifidum 07-300B and L.acidophilus 1.0357 was(11.71±0.32)and(16.12±0.57)mm,and their autolysis were(30.21±1.36)%and(39.86±2.13)%,respectively.The results showed that both of the two strains have good protease activity,and the activity of L.acidophilus 1.0357 was stronger than B.bifidum 07-300B.At the same time,the viable number of B.bifidum 07-300B and L.acidophilus 1.0357 after 8 h simulated gastrointestinal tract digestion were(6.13±0.19)lg cfu/mL and(6.05±0.18)lg cfu/mL,respectively.The hydrophobicity to xylene,chloroform and ethyl acetate of the two strains was about 30%,indicating that the two strains have good gastrointestinal tolerance and adhesion.In addition,B.bifidum 07-300B and L.acidophilus 1.0357 in mixed culture system accelerated acid production.The viable number of L.acidophilus 1.0357 in mixed culture of 1:1 ratio with B.bifidum 07-300B in,was significantly higher than that in pure culture,indicating that B.bifidum 07-300B can promote the growth of L.acidophilus 1.0357 to a certain extent,it shows that two of them have a better potential for mixing in food.(2)This paper studied the changes of pH4.6-SN,12%TCA-SN and 5%PTA-SN of Cheddar cheese during ripening stage.The results showed that the after ripening for 24 weeks,the contents of pH4.6-SN,12%TCA-SN and 5%PTA-SN in cheese contained both two kinds of probiotics were(25.72±1.56)%,(19.50±1.07)%and(10.44±0.25)%,respectively,which were higher than the control group significantly(P<0.05).Study on antioxidant activity of cheese during ripening results showed that cheese contained both of the two probiotic which DPPH scavenging,reducing power,scavenging rate of ABTS~+reach the maximum at 16 weeks,the maximum value was(31.86±1.47)%,0.517±0.011,(31.13±0.96)%,respectively,higher than that in the control group significantly(P<0.05);The number of viable bacteria in cheese contained both B.bifidum 07-300B and L.acidophilus 1.0357 after ripening for 24 weeks was(7.62±0.19)lg cfu/g,and the addition of probiotics could improve the flavor and aroma of cheese,and had no adverse effect on the overall acceptability of cheese.Therefore,it is feasible to add the two probiotics to the cheese.(3)The changes of antioxidant activity of probiotic cheese before and after simulated gastrointestinal digestion were studied.The results showed that the antioxidant activity of cheese increased significantly after digestion(P<0.05),the antioxidant index of cheese contained both B.bifidum 07-300B and L.acidophilus 1.0357 were significantly higher than other groups(P<0.05),the DPPH scavenging,reducing power,and ABTS~+scavenging rate were(82.76±3.19)%,0.828±0.021 and(44.84±1.36)%,increase 71.42%,62.35%and 51.69%respectively compared with before digestion.;The number of living probiotics decreased by 16.93%compared with that before digestion,but the content of polypeptide increased by 39.30%compared with that before digestion.The electrophoretic results showed that more small molecular weight peptides were produced after digestion,and the antioxidant activity of polypeptide that molecular weight lower than 3 kDa was the highest after digestion.Gel chromatography was used to separate them,the content of SP4components with relative molecular weight of about 823 Da is the highest,and the content of the relative molecular weight is about 823 Da,and the DPPH scavenging,reducing power,and ABTS~+scavenging rate were the highest,which were(97.53±5.86)%,0.932±0.036 and(90.36±5.37)%,respectively.Therefore,the increase of antioxidant activity after cheese digestion may be mainly related to the antioxidant peptide SP4(Mw 823 Da)produced by probiotics,pepsin and pancreatin.(4)The effect of probiotic cheese on the antioxidant activity of mice was studied.The results showed that the activity of antioxidant enzymes in the mice induced by D-galactose was lower than that in the control group significantly(P<0.05).Cheese contain both B.bifidum 07-300B and L.acidophilus 1.0357 can significantly improve the activity of antioxidant enzymes in the serum and liver tissues of mice.The SOD activity in serum and liver tissue were(276.98±15.98)U/mL and(62.97±2.91)U/mg prot,respectively.The CAT activity was(15.77±1.09)U/mL and(140.87±7.23)U/mg prot,respectively.The GSH-Px activity was(133.77±8.12)U/mL and(43.87±2.73)U/mg prot,respectively,and its antioxidant effect is close to the level of V_E.The effect of the control group was not significant(P>0.05).In addition,by measuring the content of MDA in serum and liver tissues,probiotics cheese could significantly reduce the content of MDA in serum and liver tissues(P<0.05).The results indicate that the cheese contained both B.bifidum 07-300B and L.acidophilus1.0357 can improve the antioxidant activity of mice.This study shows that B.bifidum 07-300B and L.acidophilus 1.0357 had no adverse effect on cheese quality characteristics,and significantly improved the degree of proteolysis and antioxidant activity during cheese ripening.When the probiotic cheese is digested,more antioxidative peptides will be released,which makes the oxidation activity significantly increased(P<0.05).At the same time,cheese contained both B.bifidum 07-300B and L.acidophilus 1.0357 can significantly improve the antioxidant activity of mice,showed that probiotic cheddar cheese has certain antioxidant potential. |
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